In the conventional method of whole blood collection, a needle is placed in a vein in the donor's arm and whole blood flows by gravity into a bag which holds a quantity of anticoagulant solution, which prevents the blood from clotting. When a unit of whole blood, defined in the United States as 450 milliliters (ml), has been collected, the needle is removed from the vein and the blood bag is set aside for later transfer to the processing laboratory of the blood center.
It should be noted that the ratio of anticoagulant to whole blood is approximately one to seven; thus the amount of anticoagulant in the bag is 63 ml. It should also be noted that, while the ratio of anticoagulant to whole blood is one to seven after a full unit has been collected, the ratio of anticoagulant to whole blood is considerably higher than one to seven at the beginning of the collection. The red cells flowing into the collection bag at the beginning of the collection are, therefore, subject to "anticoagulant shock", which has the effect of damaging some of the red cells. As the collection proceeds, the ratio decreases.
In the processing laboratory, a technician places the bags of whole blood into a large, swinging bucket centrifuge, which must be carefully balanced as the bags are loaded. The centrifuge is started and the bags are spun at a high rate of speed. In the first centrifugation, the red cells, which are the heaviest component, are forced to the bottom of the bag while the platelet-rich plasma, which is lighter, rises to the top. When the bags are removed from the centrifuge, they must be handled carefully so as to avoid remixing.
The technician next places each bag in an "expresser" consisting of two rigid plates that are joined by a spring loaded hinge. One of the plates is fixed and the other is moveable. The blood bag is positioned between the two plates and the spring catch released causing the moveable plate to press against the bag. A port on the top of the bag is then opened and the platelet-rich plasma is expressed into an attached, empty bag. When the technician observes that red cells are about to reach the outlet port, the expression is stopped and the tubing clamped.
If platelets are to be separated, the bags containing the platelet rich plasma are returned to the centrifuge, the load is again balanced and a second spin begins, this time at a higher speed. This spin forces the platelets to the bottom of the bag and allows the lighter plasma to rise to the top. The expression process described above is then repeated so that the platelets can be diverted to a separate bag for storage. There are other variations of these blood-component collection and separation processes, including a process for collecting a buffy coat from the blood; all of the variations use centrifugation techniques similar to those described above. Although various devices have been developed and marketed whose function is to minimize the amount of labor required in the expression of components from one bag to another, these devices do not eliminate the centrifugation step described above. Furthermore, these devices are designed to be used in the component-preparation laboratory of the blood center and not at the point of whole blood collection.
It will be appreciated, therefore, that the conventional method of centrifuging and separating components from whole blood is a labor-intensive, manual process. In addition, in order to be convenient to volunteer donors, the majority of whole blood collections take place, not in the blood center, but in mobile units that travel to other locations, such as community centers, offices and factories. Because the bags of whole blood must then be transported back to the blood center for processing and because of the need to schedule the time of laboratory personnel, many hours can elapse between the completion of the collection and the time that component separation begins.
It should be noted that, if the plasma separated from the whole blood is to be used for the production of Factor VIII for transfusion to hemophiliacs, regulations require that the plasma separation must be completed and the plasma frozen within six hours of the time of the whole-blood collection. It can be demonstrated that, the sooner the plasma is frozen, the higher will be the recovery of Factor VIII. It should be further noted that, if the plasma is to be used for transfusion as Fresh Frozen Plasma, regulations require that the separated plasma be placed at -18.degree. C. or lower within eight hours of collection from the donor. The practical consequence of these regulations is that blood banks must schedule the times of donations with the times at which laboratory personnel are available to prepare the components.
In addition to the conventional method of whole blood collection and component separation just described, individual blood components can be collected by a process called apheresis. In this process, the donor is connected to a cell separator, a needle is inserted in the donor's arm, an anticoagulant is added to the whole blood as it is drawn from the donor, and the anticoagulated whole blood is pumped into the rotor of the cell separator where centrifugal force causes the components to separate. The component that is to be retained is directed to a collection bag and the unwanted components are returned to the donor. This process of drawing and returning continues until the quantity of the desired component has been collected, at which point the process is stopped. Apheresis systems are used widely for the collection of single-donor platelets and single-donor plasma. A central feature of these apheresis devices, however, is that, while they separate blood components at the point of collection, they require that the unwanted components must be returned to the donor. This, in turn, means that apheresis devices must incorporate a variety of safety features, such as air detectors and pressure monitors, to protect the donor from harm while the donor is connected to the cell separator. Such safety mechanisms add cost and complexity to apheresis system equipment and disposables.
In contrast to apheresis systems, conventional whole blood collection systems do not return anything to the donor but, on the other hand, neither are they able to separate blood components at the site of collection. There is a need, therefore, for an improved method of whole blood collection and the preparation of components therefrom, without the complexity and expense of conventional apheresis devices, and without the labor-intensive, manual separation process described above.